Process for producing liquid hydrogen

ABSTRACT

The invention relates to an integrated process for continuous production of liquid hydrogen, comprising (a) producing gaseous hydrogen by electrolysis; and (b) liquefying said gaseous hydrogen in a hydrogen liquefaction unit, which liquefaction unit is powered by energy essentially from renewable sources; and, (c) when additional power is needed, using electrical energy generated in a process in which electrical energy and hydrogen are co-generated by an integrated electrolysis process comprising: (d) electrolysing a metal salt or mixture of metal salts and water into the corresponding metal or metals, acid or acids, and oxygen (electricity storage phase), and (e) producing gaseous hydrogen and recovering electricity in a regeneration reaction of the metal (s) and acid(s) of step (d) (regeneration phase); wherein at least part of the gaseous hydrogen generated in step (e) is used in step (b) of the process.

FIELD OF THE INVENTION

The invention relates to a process for producing liquid hydrogen and a system for said process.

BACKGROUND TO THE INVENTION

Hydrogen is an important industrial gas used in oil refining and fertilizer industries and in several other chemical processes. It is expected that hydrogen may additionally play a significant role as an energy carrier, in particular in the transportation sector.

In the absence of a domestic pipeline network, or for imports, it is expected that hydrogen in liquid form will be one of the most effective ways for its supply and distribution. However, at present hydrogen liquefaction is still expensive as well as energy intensive. Liquefaction of hydrogen involves compressing of feed hydrogen gas, several cooling steps and finally liquefaction through expansion. At present, a lot of research is being done on improving the economics of the hydrogen liquefaction process (see e.g. the European sponsored IDEALHY project which in December 2013 reported on the recently developed “Preferred Process”, see www.idealhy.eu).

Most hydrogen is currently produced via steam reforming of hydrocarbons, in particular natural gas, due to the relatively low costs of the process. Steam reforming is a strongly endothermic process. The heat needed for the process is typically provided by combusting part of the natural gas feed in a furnace.

Also other methods to produce hydrogen are known, for example by electrolysis. There are three main types of electrolysis cells, solid oxide electrolysis cells (SOEC's), polymer electrolyte membrane cells (PEM) and alkaline electrolysis cells (AEC's). SOEC's operate at high temperatures, typically around 800° C. PEM electrolysis cells typically operate below 100° C. and are becoming increasingly available commercially. These cells have the advantage of being comparatively simple and can be designed to accept widely varying voltage inputs which makes them ideal for use with renewable sources of energy such as solar PV. AEC's optimally operate at high concentrations electrolyte (KOH or potassium carbonate) and at high temperatures, often near 200° C.

In addition, methods are known for simultaneous co-generation of hydrogen and electrical energy by totally electrochemical means, which methods for example include an electricity storage phase by electrolysis of metal salts in presence of water, to metals and acids, and thereby releasing oxygen, and a generation phase whereby the produced metal & acids in storage phase are reacted to produce hydrogen and optionally electricity. The electrolysable metal is chosen from zinc, nickel, manganese. See for example U.S. Pat. No. 8,617,766.

Renewable power at (usually) remote locations is expected to be more affordable than close to markets, principally due to availability of appropriate land and better availability of the energy resource (solar, wind etc.) itself. Such remote renewable power may be a very good fit for electrolysis to produce hydrogen as it generates an affordable renewable energy molecule. Where renewable power supply is not sufficiently available, power from conventional sources (e.g. power generated by gas turbines and delivered through the grid) may also, or in addition, be used.

In particular renewable power generated from wind and solar sources suffers from the intermittent availability of these natural resources. At such locations with unstable power supply the production of hydrogen, and in particular the liquefaction of hydrogen, is not as effective as at locations where the production and liquefaction processes can continuously be run and the expensive liquefaction plant as a result can be highly utilized.

The present invention provides a solution to the problem of under-utilization of hydrogen production and hydrogen liquefaction plants, in particular in remote locations with unstable power supply. Further the present invention solves the problems of intermittency in hydrogen production and liquefaction plants at locations where power supply comes, at least in part, from renewable energy sources, and in particular from wind and solar energy.

SUMMARY OF THE INVENTION

It has now been found that by integrating at remote locations hydrogen production and liquefaction processes with a method that allows intermittent hydrogen and electricity storage, a solution is provided to the above mentioned problems. Accordingly, the present invention provides an integrated process for continuous production of liquid hydrogen, comprising

(a) producing gaseous hydrogen by electrolysis; and (b) liquefying said gaseous hydrogen in a hydrogen liquefaction unit, which liquefaction unit is powered by energy essentially (i.e. at least 80%, preferably at least 90%, most preferred 100%) from renewable sources; and, (c) when additional power is needed, using electrical energy generated in a process in which electrical energy and hydrogen are co-generated by an integrated electrolysis process comprising: (d) electrolysing a metal salt or mixture of metal salts and water into the corresponding metal or metals, acid or acids, and oxygen (electricity storage phase), and (e) producing gaseous hydrogen and recovering electricity in a regeneration reaction of the metal(s) and acid(s) of step (d) (regeneration phase); wherein at least part of the gaseous hydrogen generated in step (e) is used in step (b) of the process.

This process of the present invention is ideally suited for liquid hydrogen manufacturing by allowing the expensive liquefaction unit to run on a continuous basis while providing hydrogen and additional electricity on demand basis, despite the fact that the basic renewable energy source is only intermittently available.

Moreover, the integration of the electrolysis process can advantageously be done at one or more locations in the production and liquefaction process. For example, the power generated in the electrolysis may provide (part of) the power needed in the liquefaction cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1, a process according to the invention is schematically shown.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention the process comprises first feeding renewable (wind, solar etc.) intermittent electricity to an integrated electrolysis process set-up.

The integrated electrolysis process is defined as an electrolysis process comprising two distinct steps:

-   -   (d) an electricity storage step wherein a metal salt or mixture         of metal salts (the metal salt being selected from ZnSO₄, MgSO₄,         MgCl₂, and the like; preferably the metal salt is ZnSO₄) is         reacted with water to deposit metal on the electrode and to form         acid (H₂SO₄, HCl etc.) while releasing oxygen, which reaction is         driven by intermittent, optionally renewable, electricity;     -   (e) a regeneration step wherein the deposited metal on the         electrode is reacted with the acid produced in step (d) to         release hydrogen and re-synthesize the original metal salt(s),         which may be done in the presence of a suitable catalyst.         Optionally, in this step (part of) the stored energy can be         regenerated as electricity (in addition to hydrogen).

Methods for co-generation of electric energy and hydrogen by a two-step electrolysis process as described here are known in the art, e.g. as disclosed in U.S. Pat. No. 8,617,766.

By pursuing the above two step integrated electrolysis process, it is possible to separate the charging (electricity storage) step (d) from discharging (regeneration) step (e). In this way, the energy and hydrogen storage capability provides an additional source of electricity and hydrogen when compared to conventional electrolysis processes whereby hydrogen is released simultaneously when feeding power to an electrolyser.

Additionally, as an advantage of the process according to the invention, both the hydrogen and electricity product of step (e) can be individually produced as needed “on-demand”. The process of the present invention thus advantageously allows that the equipment can be arranged in such a way that hydrogen may be produced all day and electricity only when needed, for example at night-time (for example in case of a solar power fed system).

After the first step of feeding renewable intermittent electricity to the integrated electrolysis process set-up, the produced hydrogen and/or electricity is subsequently fed to the hydrogen liquefaction unit, favourably co-located with the integrated electrolyser. In the hydrogen liquefaction unit, electricity is needed as an input to drive the compressors and the cooling units which form the core of liquefaction process.

By using the integrated process of the invention, it is possible to run the expensive hydrogen liquefaction unit in a stable and continuous operation mode, which is desired in order to make the best use of this capital investment. This would otherwise not be possible with only direct feed of intermittent electricity and/or intermittent hydrogen feed.

Typically, the hydrogen liquefaction unit will run on renewable electricity when available, while electricity regenerated from the electrolyser in step (e) is used as a back-up in the intermittent periods (i.e. in case of solar electricity during night time or bad weather conditions).

In a further embodiment, in case renewable electricity is the only source of electricity, optionally also additional sources of electricity supply (for example electric storage devices such as batteries) may be used as back-up when the renewable power source is not available and/or electricity regenerated from the electrolyser is not enough for supplying sufficient power to the hydrogen liquefaction unit.

In an embodiment of the invention, in the process comprising the integrated electrolysis process and hydrogen liquefaction process, gaseous hydrogen is optionally stored in a hydrogen storage unit in between the electrolyser (i.e. after step (e)) and the hydrogen liquefaction unit (i.e. before liquefying the hydrogen) to manage a stable hydrogen supply to the liquefaction unit.

Liquefaction of hydrogen and liquefaction cycles suitable for hydrogen liquefaction are known in the art. Any suitable liquefaction cycle known in the art may be used, including the Claude cycle, Brayton cycle, Joule Thompson cycle and any modifications or combinations thereof.

A further embodiment of the invention relates an integrated system for continuously producing liquid hydrogen, comprising an energy inlet for feeding energy from renewable sources into an electrolysis system for co-generation of electrical energy and hydrogen, which comprises an energy storage part and a regeneration part, wherein the regeneration part of the electrolysis system has an outlet for hydrogen that is connected to a hydrogen liquefaction unit and wherein the regeneration part of the electrolysis system has an outlet for electricity produced in the electrolysis system that is connected to an energy inlet into the hydrogen liquefaction unit for power supply. The system may advantageously comprise a hydrogen storage unit for intermittent storage of gaseous hydrogen. Further, the system may favourably comprise a battery for storage of power for providing additional power at moments of very high demand.

It is to be noted that a person skilled in the art will understand that for a designated liquid hydrogen production facility the above discussed electrolyser process integration options will need to be optimized depending on the site location, infrastructure and specific application. Thus, multiple process schemes can be constructed around the basic building blocks of a hydrogen liquefaction facility fed by the process comprising an integrated electrolyser according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1, an example of the process according to the invention is schematically shown, which should not be interpreted as limiting the invention:

energy (e⁻), essentially from renewable sources, is fed via an inlet (1) into an integrated electrolysis system (2), which comprises an energy storage part (3) and a regeneration part (4); in the energy storage part of the electrolysis system a metal salt (MX) and water are converted into the corresponding metal (M), the corresponding acid (HX) and oxygen; when needed (“on demand”), in the regeneration part (4) the metal salt is formed again and gaseous hydrogen (GH₂) is released via outlet (5), while optionally also producing electricity; the gaseous hydrogen is introduced via inlet (6) into the hydrogen liquefaction unit (7); the electricity from the electrolysis system may on demand be released via outlet (8) to be used in the hydrogen liquefaction unit (7); energy (e), essentially from renewable sources, is also used to power the hydrogen liquefaction unit (7) via inlet (9); electricity may also be stored in a battery (10) for use to supply to the hydrogen liquefaction unit (7) in high demand situations or to supplement in case of low availability of the renewable energy; liquid hydrogen (LH₂) is exported from the system via line (11). 

1. An integrated process for continuous production of liquid hydrogen, comprising: (a) producing gaseous hydrogen by electrolysis; (b) liquefying said gaseous hydrogen in a hydrogen liquefaction unit, which liquefaction unit is powered by energy essentially from renewable sources; and, (c) when additional power is needed, using electrical energy generated in a process in which electrical energy and hydrogen are co-generated by an integrated electrolysis process comprising: (d) electrolysing a metal salt or mixture of metal salts and water into the corresponding metal or metals, acid or acids, and oxygen (electricity storage phase), and (e) producing gaseous hydrogen and recovering electricity in a regeneration reaction of the metal(s) and acid(s) of step (d) (regeneration phase); wherein at least part of the gaseous hydrogen generated in step (e) is used in step (b) of the process.
 2. The process of claim 1, wherein the metal salt or mixture of metal salt is/are selected from ZnSO₄, MgSO₄, and/or MgCl₂, and the like.
 3. The process of claim 2, wherein the metal salt is ZnSO₄.
 4. The process of claim 1, wherein the hydrogen and electricity products of step (e) are individually produced as needed “on-demand”.
 5. The process of claim 1, wherein additional sources of electricity supply are used as back-up when the renewable power source is not available and/or electricity regenerated in step (e) is not enough.
 6. The process of claim 1, wherein gaseous hydrogen is stored after step (e) and before liquefying the hydrogen.
 7. An integrated system for continuously producing liquid hydrogen, comprising an energy inlet for feeding energy from renewable sources into an electrolysis system for co-generation of electrical energy and hydrogen, which comprises an energy storage part and a regeneration part, wherein the regeneration part of the electrolysis system has an outlet for hydrogen that is connected to a hydrogen liquefaction unit and wherein the regeneration part of the electrolysis system has an outlet for electricity produced in the electrolysis system that is connected to an energy inlet into the hydrogen liquefaction unit for power supply.
 8. The integrated system of claim 7, further comprising a hydrogen storage unit for intermittent storage of gaseous hydrogen.
 9. The integrated system of claim 7, further comprising a battery for storage of power,
 10. The process of claim 2, wherein the hydrogen and electricity products of step (e) are individually produced as needed “on-demand”.
 11. The process of claim 2, wherein additional sources of electricity supply are used as back-up when the renewable power source is not available and/or electricity regenerated in step (e) is not enough.
 12. The process of claim 2, wherein gaseous hydrogen is stored after step (e) and before liquefying the hydrogen.
 13. The process of claim 3, wherein the hydrogen and electricity products of step (e) are individually produced as needed “on-demand”.
 14. The process of claim 3, wherein additional sources of electricity supply are used as back-up when the renewable power source is not available and/or electricity regenerated in step (e) is not enough.
 15. The process of claim 3, wherein gaseous hydrogen is stored after step (e) and before liquefying the hydrogen. 